The present invention generally relates to the coupling of a harmonic drive or strain wave gearing set to a worm drive, where the harmonic drive or strain wave gearing serves as the input.
Harmonic drives or strain wave gearing has been used for some time. For example, U.S. Pat. Nos. 2,906,143 and 2,983,162 disclose harmonic drives or strain wave gearing. Both of these patents are hereby incorporated herein by reference in their entirety. Generally speaking, a harmonic drive or strain wave gearing is a motion transmitting mechanism, wherein relative motion occurs between an internal gear and a cooperating external gear. More specifically, a harmonic drive or strain wave gearing operates by deformation of a flexible gearing member having fewer gear teeth than a mating gear. The deformation combined with the difference in gear teeth creates relative motion between the flexible gearing member and the mating gear.
Worm gearing has also been used for quite some time. For example, U.S. Pat. No. 6,386,059 discloses a worm drive. A worm drive permits a ninety-degree angle between the input and output of the gear box at a variety of ratios. In contrast, harmonic drive or strain wave gearing provides an input and an output which are coaxial at high reduction ratios. Planetary primaries are ubiquitous in their use on worm gearing. However, planetary primaries are large, inefficient and have backlash.